World Small Animal Veterinary Association World Congress Proceedings, 2003

Colin F. Burrows, B.Vet.Med., PhD, MRCVS, DACVIM

College of Veterinary Medicine, University of Florida Gainesville, FL, USA

The term "acute abdomen" is used to describe an often multietiologic clinical syndrome characterized by the sudden onset of intense abdominal pain and associated signs which include: shock, vomiting, diarrhea, changes in gastrointestinal peristaltic activity, fever, anorexia and dyspnea. Immediate supportive therapy is often indicated to preserve the life of the patient while a diagnosis is pursued. Decisions about the overall management of the patient can only be made after establishment of an accurate diagnosis. Even with a searching history and physical examination the etiology may tax the diagnostic acumen of even the most experienced practitioner. Diagnostic laboratory and radiographic procedures are essential.

An acute abdominal problem can usually be classified into one of three categories, each dictating its own course of management:

1. Intra-abdominal lesions usually requiring urgent surgical intervention after a period of resuscitation and stabilization.

The clinician should be able to quickly determine whether immediate intervention is required. At presentation, the complaint should be noted and a brief history taken while carrying out a rapid evaluation of the patient. This evaluation should include the patient's attitude, mucous membrane color, heart rate, pulse quality, respiratory effort, and response to abdominal palpation. If the patient is in shock or bleeding, supportive therapy should be initiated and a more detailed history obtained at a later opportunity.

History

This is always the first, and often the most important aid to diagnosis. The age, breed, sex, environment, onset, course, nature and duration of signs should all be considered. It is important to note if the onset is spontaneous or follows trauma.

The presenting complaint for an animal with an acute abdomen may include acute abdominal pain or distension, vomiting, diarrhea, anorexia, weakness or collapse. The signalment may indicate the likely cause of the problem; for example, young animals are more likely to ingest foreign bodies, develop intussusceptions or contract viral enteritis.

Acute abdominal diseases in the adult include: decompensated chronic infections, pancreatitis, vascular occlusive disease and intestinal obstruction or abdominal organ displacement caused by a tumor. Older obese female dogs may have an increased risk of pancreatitis. Cats tend to ingest linear foreign bodies whereas deep chested dogs such as great Danes, Wolfhounds and Irish setters are more likely to develop gastric dilatation volvulus. German shepherds and Labrador and golden retrievers are commonly affected with splenic neoplasia.

Knowledge of the previous medical history such as exposure to infectious disease, trauma or previous abdominal surgery (which may suggest a paralytic ileus or obstruction from adhesions) is often helpful. Chronic weight loss may suggest an intra-abdominal tumor. Over-eating or the ingestion of spoiled or frozen food may precipitate acute gastric dilatation or acute hemorrhagic gastroenteritis. A history of mast cell tumors or corticosteroid or non-steroidal anti-inflammatory drug therapy increases the risk for gastrointestinal ulceration. The potential for toxin exposure can be a crucial part of the history.

Physical Examination

The patient should be assessed for mental attitude (alertness), posture, and ability to walk. Dogs with abdominal pain may stand with an arched posture or "praying position" that alleviates abdominal pressure. Cats may stand with their heads extended and elbows abducted, signs that may be confused with respiratory distress.

Points to be noted during the evaluation include the patient's body temperature, hydration status, heart rate and rhythm, pulse quality, mucous membrane color, and capillary refill time. The thorax should be carefully auscultated and a thorough oral examination performed, including looking under the tongue. Oral examination may require sedation or anesthesia. Patients unwilling to allow an oral examination are often the ones that need it most. A rectal examination is also important. The prostate should be carefully evaluated in male dogs and the urethra palpated in both males and females. A rectal examination may also be indicated in cats but should be withheld until the animal is sedated or anesthetized. It is important to evaluate the character of the feces during the rectal examination.

Abdominal Evaluation

This is one of the most important parts of the physical examination and has to be a thorough exploration of each organ system. Visual inspection of the abdomen may tend to localize signs of trauma or of distension which can be symmetrical or asymmetrical. Abdominal distension may be caused by the six F's (fat, food, fluid, flatus, feces, fetus) or by a tumor.

Depending upon the quantity of gas, percussion may yield signs of tympany indicating mechanical obstruction or acute gastric dilatation. Free peritoneal fluid may be identified by ballottement. Palpation may be difficult because of protective spasm of the abdominal muscles in response to pain. Spinal cord trauma and other, nonsurgical, conditions also result in a rigid abdomen. Foreign bodies, intussusception, calculi, enlarged organs and abdominal masses may be palpated in the cooperative patient. Other important findings include identifying fluid or gas filled bowel loops, a plicated or thickened intestinal segment, or a mass (tumor, intussusception or foreign body).

Differential Diagnosis

Each of the patient's problems should be considered and differential diagnoses identified and ranked according to their probability based on the signalment, history and physical findings. A complete list of differential diagnoses is listed in Table 1.

Clinical Laboratory Examination

The number of laboratory tests utilized depends upon a selection made in the light of the history and physical findings. Some studies should be carried out on all patients; others are indicated only to confirm a provisional diagnosis.

Studies that should be considered routinely include: the packed cell volume and total solids (PCV/TS), red cell count, total and differential white cell count, creatinine or BUN, glucose, urinalysis and fecal examination. Hypoglycemia may suggest sepsis. A low PCV may indicate hemorrhage, although anemia can result from other disorders. Anemia from hemorrhage may not be immediately evident because of splenic contraction or volume depletion. A low protein suggests decreased production or losses due to gastrointestinal, renal or peritoneal disease. Azotemia may also be due to renal failure, shock or sepsis.

If available, a full serum chemistry profile can help evaluate abdominal disease, although many abnormal results are non-specific. Hepatic enzyme activities may be increased because of hepatic injury, sepsis, hypoxia or pancreatitis. A complete white blood cell count helps determine if inflammation is present which can be associated with sepsis, or peritonitis. The WBC differential count may suggest an acute, chronic or degenerative response. Urinalysis may provide information about the patient's urine concentrating ability and hydration status, the presence or absence of urogenital hemorrhage or trauma, or the potential source of infection e.g., pyelonephritis.

Paracentesis and abdominal lavage are valuable diagnostic aids in the evaluation of abdominal disease and should be considered in patients which have had abdominal trauma or have ascites. Cytological evaluation of any fluid obtained often provides valuable clues to diagnosis.

Radiographic Examination of the Abdomen

Radiographic examination of the abdomen often plays a valuable and important part in the early diagnosis, prognosis and management of the patient with acute abdominal disease.

Survey radiographs of the thorax and abdomen may reveal pathologic anatomy with a minimum of manipulation of the patient and with results available in a much shorter period of time than data from many laboratory tests.

2. Pneumocystogram or cystogram defines and determines the integrity of the bladder and urethra.

3. An IVP or renal arteriogram determines the integrity of the kidneys and ureters.

4. A pneumoperitoneum can outline the borders of otherwise poorly defined abdominal organs.

Ultrasound Examination

Ultrasonography is another very useful imaging technique. An ultrasound examination can help distinguish surgical from non surgical disease.

Exploratory Laparotomy

The decision to perform surgery in the patient with an acute abdomen can be challenging. Sometimes the results of diagnostic testing fail to yield a clear diagnosis and exploratory laparotomy must be considered a diagnostic test. There are a number of intra-abdominal lesions that are difficult to recognize or positively define without abdominal exploration. This is particularly true when the signs are obscure or if they recur with an increase in severity or frequency.

Treatment

Treatment of the patient with the acute abdomen should always be predicated on correction or amelioration of the underlying disease. There are nevertheless, certain fundamental principles that must be applied to all patients. These are the treatment of shock, antimicrobial therapy, ensuring adequate tissue oxygenation and protection of the gastric mucosal barrier.

Fluid loss or sequestration is common in many patients with acute abdominal disease and fluid therapy and correction of electrolyte disturbances are critical. Diseases that compromise gastrointestinal integrity can increase the likelihood of bacterial translocation from the gut, decrease venous return, or cause portal hypertension or septicemia that predispose the patient to endotoxemia and shock. Intravenous fluid therapy with a balanced electrolyte solution containing supplemental potassium is critical in many if not all patients. The administration of blood products or colloids may also benefit critically ill patients.

While culture and antimicrobial sensitivity testing are always indicated in instances of infection, it is prudent to begin empirical antibiotic therapy in a systemically ill patient while awaiting test results. Appropriate choices of antibiotics include cefazolin sodium or amoxicillin trihydrate clavulanate potassium. Combination therapy with ampicillin sodium and enrofloxacin or ampicillin sodium and amikacin sulfate may be used for more coverage of gram-negative infections. Metronidazole or clindamycin can be used for expanded anaerobic coverage.

The gastric mucosal barrier can be disrupted in many patients with acute abdominal disease. This can occur as a result of hypovolemia or of sepsis which both cause decreased gastric mucosal blood flow. Portal hypertension can cause a congestive gastropathy with similar results. The end result is diffuse gastric erosion or ulceration with loss of blood and tissue fluid. This can be minimized with aggressive prophylactic therapy early in the disease process. Intravenous ranitidine is a good initial choice with an oral proton pump inhibitor in severe disease. Oral sucralfate is also beneficial since it forms a protective shield over the eroded mucosa.

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